The present invention is directed to a vapor-air steam engine which operates at high pressure and utilizes a working fluid consisting of a mixture of fuel combustion products and steam with a minimal amount of excess compressed air. The invention is further directed to processes for producing electrical energy, usable shaft horsepower and/or large quantities of steam in a fuel burning system at high efficiency and low specific fuel consumption, while generating insignificant amounts of environmental pollutants (NOx, CO, particulates, unburned fuel). The invention is still further directed to the production of potable water while generating electrical power without polluting the environment or significantly reducing the efficiency or increasing the fuel consumption.
Internal combustion engines are generally classified as either constant volume or constant pressure. Otto cycle engines operate by exploding volatile fuel in a constant volume of compressed air while diesel cycle engines burn fuel in a modified cycle, the burning being approximately characterized as constant pressure.
External combustion engines are exemplified by steam engines, steam turbines and gas turbines. It is well known to supply a gas turbine with a gaseous working fluid generated by combusting a fuel with compressed air and to operate various motor devices from energy stored in this high pressure gaseous stream. In these devices, temperature control is usually the result of feeding large quantities of excess compressed air.
It is also known to burn fuel in a chamber and exhaust the combustion products into a working cylinder or chamber, sometimes with the injection of small quantities of water or steam. These may also be classified as external combustion engines.
Some other devices have been proposed in which combustion chambers are cooled by addition of water or steam provided either internally or externally. Still another form of apparatus has been proposed for operation on fuel injected into a combustion cylinder as the temperature falls, having means to terminate fuel injection when the pressure reaches a desired value.
Each of these prior engines has encountered difficulties which limit their general adoption as a power source for the operation of prime movers. Among these difficulties have been the inability of such an engine to meet sudden demand and/or to maintain a constant working temperature or pressure as may be required for efficient operation of such an engine.
Furthermore, control of such engines has been inefficient, and the ability of the gas generator to maintain itself in standby condition has been wholly inadequate. In all practical applied engine configurations the requirement for cooling the confining walls of the work cylinders has resulted in loss of efficiency and a number of other disadvantages previously inherent in internal combustion engines.
The present invention overcomes the limitations of the prior art described above. First, the requirement of large amounts of excess compressed air or external liquid cooling is eliminated by injecting water directly into the combustion chamber to control the temperature of the resulting working fluid. When water is injected it is converted instantaneously into steam in the combustion chamber, and it becomes a component of the working fluid itself, thus increasing the mass and volume of the working fluid without mechanical compression.
In the present invention, independent control of the a) combustion flame temperature b) combustion chamber temperature profile by liquid water injection and c) fuel to air ratio allows the physical properties of the working fluid to be optimized for high efficiency operation. Reducing or eliminating excess air, thus limiting the availability of excess oxygen, and controlling the flame temperature and combustor temperature profile also prevents the formation of NOx, and favors the complete conversion of burning fuel to CO2, minimizing CO production.
The present invention also utilizes high pressure ratios as a way of increasing efficiency and horsepower while simultaneously lowering specific fuel consumption (xe2x80x9cSFCxe2x80x9d). When water is injected and converted into steam in the combustion chamber of the present invention, it acquires the pressure of the combustion chamber. It should be noted that the pressure of the combustion chamber is acquired by the steam irrespective of the pressure ratio of the engine. Thus, a higher pressure ratio can be obtained in the engine without expending additional work for performing compression for new steam or water injection. Because of the injection of massive amounts of water in the present invention, there is no need to compress more air than needed for combustion, this excess air typically used in prior art systems for cooling. The elimination of this requirement results in an enormous energy savings to the system and a significant increase, without additional consumption of fuel, in the available shaft horsepower without increasing turbine speed.
Water injection, as taught in the present invention, provides several advantages over the prior art. First, a minimal amount of additional work is required to pressurize water above the combustion chamber pressure. In steam injection system significant work must be expended to raise the steam to a pressure above that of the combustion chamber. Likewise, excess air requires additional work be expended to raise the feed air to higher pressures to produce additional working fluid mass. Furthermore, when water is injected and converted to steam in the present invention, it acquires the pressure of the combustion chamber without additional work. This steam also has constant entropy and enthalpy.
In the present invention excess (waste) heat from combustion is used to convert injected water to steam, thus increasing the working fluid pressure and mass of the working fluid without mechanical compression of excess air. In contrast, in a typical Brayton Cycle Turbine, 66%-75% of the mechanically compressed air is used to dilute the products of combustion in order to reduce the temperature of the working fluid to the desired Turbine Inlet Temperature (xe2x80x9cTITxe2x80x9d).
The steam generated by vaporization of the injected water can at least double the mass of the combustion generated working fluid and increase the net horsepower by 15% or more. Therefore, the water can be seen to serve as a fuel in this new thermodynamic system because it supplies pressure, mass, and energy to the system, resulting in an increased efficiency of the present system.
The cycle of the present invention may be open or closed with respect to water. That means that the air and water may be exhausted (open) or recovered and recycled (closed). Desalination or water purification can be a byproduct of electric power generation from a stationary installation or water borne ships, where the cycle is open as to air but closed as to the desalinated water recovery. Marine power plants, industrial applications, drinking water and irrigation water clean up and recovery systems are also viable applications.
The present cycle can also be employed in the closed cycle phase in mobile environments, e.g. autos, trucks, buses, rail locomotives, marine craft, commuter aircraft, general aviation and the like.
One of the objectives of this invention is to provide a new, thermodynamic power cycle, which can operate in an open or closed mode, that compresses a stoichiometric amount of air and combusts fuel with the air so as to provide efficient, clean, pollution free power.
It is also an object of this invention to completely control the temperature of combustion within a combustor through the employment of the latent heat of vaporization of water without the necessity to mechanically compress excess (dilution) air for cooling.
A further object of this invention is to reduce the air compressor load in relation to a power turbine used in the engine so that a smaller compressor can be used and slow idling and faster acceleration can be achieved.
A further object of this invention is to separately control the turbine inlet temperature (TIT) on demand.
Another object of this invention is to vary the composition and temperature of the working fluid on demand.
It is also an object of this invention to provide sufficient dwell time of the reactants in the combustion chamber to permit stoichiometric combustion, chemical bonding, and time for complete reaction and quenching, resulting in chemical equilibrium.
It is also an object of this invention to combust and cool the products of combustion in a manner which will prevent the formation of smog causing components such as NOx, unburned fuel, CO, particulates, CO2 dissociation products, etc.
It is also an object of this invention to provide a combustion system with 100% conversion of one pound of chemical energy to one pound of thermal energy.
It is also an object of this invention to operate the entire power system as cool as possible and still operate with good thermal efficiency.
It is also an object of this invention to provide a condensing process in order to cool, condense, separate, and reclaim the steam as condensed, potable water.
It is also an object of this invention to provide an electric power generating system which uses nonpotable water as its coolant and produces potable water as a byproduct of the electric power generation.
It is also an object of this invention to provide a new cycle which alternatively provides a modified Brayton cycle during one mode of engine operation, a vapor air steam cycle during a second mode of engine operation and a combined cycle during a third mode.
It is also an object of this invention to provide a combustor for use with any turbine power generating system such that the power system produces electrical energy at a greater efficiency and reduced specific fuel consumption when compared with currently available systems using currently available combustors.
It is also an objective of this invention to provide a combustor which can be retrofit into current hydrocarbon fuel burning systems replacing currently used combustors and eliminating the need for pollution abatement equipment (catalytic converts, reburns, scrubbing systems) while increasing operating efficiency and decreasing pollution in exhaust streams.
It is also an object of the invention to provide a turbine power generation system which provides significantly increased usable shaft power (net usable power) when compared with a Brayton cycle system burning an equivalent amount of fuel.
It is also an object of this invention to provide a power generating system which produces electrical energy at an overall efficiency significantly greater than 40%.
It is also an objective to provide a power generating system which burns hydrocarbon fuels in a more efficient manner to produce less green house gases (CO2).
It is also an objective to efficiently provide large quantities of steam at any temperature and pressure desired.
In accordance with one exemplary embodiment of the present invention, referred to as the VAST cycle, an internal combustion engine is described. This engine includes a compressor configured for compressing ambient air into compressed air having a pressure greater than or equal to six atmospheres, and having an elevated temperature. A combustion chamber connected to the compressor is configured for staged delivery of compressed air from the compressor to the combustion chamber. Separate fuel and liquid injection controls are used for injecting fuel and liquid water respectively into the combustion chamber as needed and where needed. The amount of compressed air, fuel and water injected, the pressure of the compressed air, fuel and water injected, the temperature of the compressed air and fuel injected, and the temperature of the injected water and the point of injection into the combustor are each independently controlled. As a result, the average combustion temperature and the fuel to air ratio (F/A) can also be independently controlled. The injected fuel and a controlled portion of the compressed air are combusted, and the heat generated transforms the injected water into a vapor. When the injected water is transformed into a vapor the latent heat of vaporization of the water reduces the temperature of the combustion gases exiting the combustor. An amount of water significantly greater than the weight of the combusted fuel is used. However, the mass of air feed to the system is significantly reduced. As a result, the mass flow of combustion generated working fluid maybe varied from 50% to greater than 200% of mass flows in current systems using the same amount of fuel under most operating conditions.
A working fluid consisting of a mixture of a small amount of the unburnable 79% non-oxygen components of the compressed air, fuel combustion products and water vapor is thus generated in the combustion chamber during combustion at a predetermined combustion temperature and combustor temperature profile. Substantially all of the temperature control is provided by the latent heat of vaporization of the water. Any excess is provided only to assure complete combustion and is not provided for cooling purposes. This working fluid can then be supplied to one or more work engines for performing useful work. Alternatively, the working fluid, which is high temperature, high pressure steam can be used directly, such as injection in oil wells to increase flow, as a heat source for distillation towers or other equipment which utilize steam for operation.
In more specific embodiments of the present invention, an ignition sparker is used to start the engine. The engine may also be operated either open or closed cycle; in the latter case, a portion of the working fluid exhaust may be recuperated. The flame temperature and combustion chamber temperature profile are monitored using temperature detectors and thermostats located throughout the combustor.
Further, a computerized feedback control system may be used to monitor the gaseous components of the exhaust stream and operating conditions and feed rates can be automatically adjusted to minimize NOx and CO in the exhaust.
When the present invention is used, the combustion temperature is reduced by the combustion control means so that stoichiometric combustion and chemical reaction equilibrium are achieved in the working fluid. All chemical energy in the injected fuel is converted during combustion into thermal energy and the vaporization of water into steam creates cyclonic turbulence that assists molecular mixing of the fuel and air such that more complete combustion is effectuated. The injected water absorbs all the excess heat energy, reducing the temperature of the working fluid to the maximum desired operating temperature of the work engine. When the injected water is transformed into steam, it assumes the pressure of the combustion chamber, without additional work for compression and without additional entropy or enthalpy. The careful control of combustion temperature prevents the formations of gases and compounds that cause or contribute to the formation of atmospheric smog and, by virtue of the increased operating efficiency, reduces the amount of green house gases generated per usable energy produced.
In another embodiment of the present invention, electric power is generated using nonpotable water as its coolant, potable water being produced as a byproduct of the power or steam generation.
In a third embodiment of the present invention (a new cycle) the engine can operate in three different modes. When the engine is operated in excess of a first predetermined rpm (i.e. at a high RPM), water injection and the amount of compressed air combusted is kept constant as engine rpm increases. At an interim RPM, i.e. between a first (high) and second (low) predetermined rpm, the water to fuel ratio is increased as the amount of excess air is decreased. When the engine is operated at various speeds below a second predetermined rpm (i.e. a low RPM), the ratio of injected water to fuel is held constant and the amount of compressed air combusted is held constant, excess air being substantially eliminated.
The use of this new cycle results in increased horsepower at a lower rpm, slow idle, fast acceleration and combustion of up to 95% of the compressed air at low rpm.
A more complete understanding of the invention and further objects and advantages thereof will become apparent from a consideration of the accompanying drawings and the following detailed description. The scope of the present invention is set forth with particularity in the appended claims.